Method of fuse manufacture and a battery pack containing that fuse

ABSTRACT

The method of fuse manufacture has a step to fabricate a metal plate with an overall long narrow shape, with a plurality of rows of connecting pieces having separated tips and connected aft ends, and with the tip of each connecting piece arranged in a straight line; a step to connect the tips of adjacent connecting pieces by welding wire to the connecting piece tip regions which are arranged in a straight line; a step to treat two adjacent connecting pieces as a unit, to cut the wire between each two-connecting piece unit for separation, and to detach each individual connecting piece; and a step to bend the wire, connecting each cut two-connecting piece unit, to form the pair of connecting pieces into a straight line.

This application is based on application No. 115753 filed in Japan onApr. 17, 2000, the content of which incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

This invention relates to a method of manufacturing a fuse which meltsand breaks due to heating with excessive current flow, and to a batterypack which contains that fuse.

A fuse shuts off current flow by melting open due to heat generated byexcessive current flow. A fuse is heated by Joule heating. Joule heatingincreases in proportion to the square of the current times theelectrical resistance of the fuse. Consequently, as current flowincreases, Joule heating increases abruptly heating the fuse to hightemperatures. The temperature at which a fuse blows is determined by themetal used. Thus, a fuse heats and melts open at a prescribed currentflow and shuts off that current.

A battery pack contains a fuse to protect the batteries from excessivecurrents. A fuse is connected in series with the batteries and is meltedopen by excessive current. A battery pack which utilizes a lead In thedual role as a fuse has also been developed (Japanese Patent ApplicationSHO 55-141448, 1980). The battery pack cited has a lead formed with anarrow section to melt open with excessive current.

In addition, the present inventor developed a fuse using laminates, suchas bi-metal and tri-metal laminates of metals with different thermalexpansion rates, to improve the breaking characteristics of a fuse withthe previously cited structure (Japanese Patent Application HEI11-154714, 1999). When this fuse is heated by excessive current,mechanical deformation stress, due to differences in thermal expansionrates of the laminated metals, acts on the section which blows.Consequently, this fuse has the characteristic of blowing quickly as aresult of mechanical deformation stress acting on the fuse when heatedby excessive current.

However, a fuse of this structure has the drawback of high materialscost because of the use of bi-metals or tri-metals. Further, in a fuseof this type with the structure shown in FIG. 1, the current at whichthe fuse blows is determined by the cross sectional area of a narrowsection. Therefore, it is necessary to cut this section significantlythin. This is because the shut down current for a battery pack is smallat only a few amperes.

A fuse made with a narrowly cut section has the drawback that it can beeasily broken by mechanical shock, for example by dropping duringbattery pack assembly or after being assembled in a battery pack. If thefuse mechanically breaks, the battery pack becomes completely uselessafter that. Consequently, although it is important for a fuse installedin a battery pack to reliably melt open with excessive current flow, itis also important for the fuse not to break open as a result ofmechanical shock.

Further, for a fuse with a locally narrow section as shown in FIG. 1,there are limitations to the width of the narrow region imposed bymanufacturing practicality. For example, it is extremely difficult tofabricate this type of fuse for a fuse blowing current on the order of3A. Therefore, this type of fuse has the drawback that it cannot beinstalled in a low capacity battery pack. Since the width of the narrowsection must be made still narrower as the fuse blowing current becomessmaller, this type of low current fuse has the further drawback that itis becomes easier to break by mechanical shock.

The present invention was developed to resolve these types of drawbacks.Thus it is a primary object of the present invention to provide a methodof fuse manufacture and a battery pack containing that fuse wherein thefuse can be inexpensively manufactured in quantity, is blown reliablywith excessive current, is difficult to break with mechanical shock, andin particular, can be made resistant to mechanical shock for low fuseblowing currents.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

SUMMARY OF THE INVENTION

The present invention manufactures a fuse by a step to fabricate a metalplate with an overall long narrow shape, with a plurality of connectingpieces having separated tips and connected aft ends, and with the tip ofeach connecting piece arranged in a straight line; a step to connect thetips of adjacent connecting pieces by welding wire to the connectingpiece tip regions which are arranged in a straight line; a step to cutthe wire between each pair of two adjacent connecting pieces and todetach each individual connecting piece; and a step to bend the wireconnecting each cut pair of connecting pieces, attached at both sides ofthe wire, in a direction which separates both ends of the connectingpieces.

The method above can inexpensively manufacture fuses in quantity, canproduce a fuse that blows reliably with excessive current but isdifficult to break with mechanical shock, and in particular, the methodhas the characteristic that a fuse can be made to blow at low currentsand be strong with respect to mechanical shock. This is because themethod of manufacture above has a step to fabricate a metal plate with aplurality of connecting pieces having separated tips and connected aftends, a step to connect the tips of adjacent connecting pieces bywelding wire to the connecting piece tip regions, a step to cut the wirebetween each pair of two adjacent connecting pieces and to detach eachindividual connecting piece, and a step to bend the wire connecting eachcut pair of connecting pieces in a direction which separates both endsof the connecting pieces.

Further, the method above can manufacture with extreme simplicity a fusestructure having connecting pieces at both ends of a wire, and moreovercan efficiently manufacture these fuses in quantity. Consequently, fusemanufacturing cost can be reduced, and they can be inexpensivelymanufactured in quantity.

Further, since a fuse manufactured by the method above is configuredwith wire as the narrow melting and breaking region, it is stronger withrespect to mechanical shock than a fuse of the type shown in FIG. 1.This is because the metal wire material itself is strong, and inaddition the wire can resiliently deform. Further, since the wire isbent, this bent region can absorb and dissipate mechanical shock. Inparticular, since a folded back configuration for connecting piece tipsallows both ends of the wire to be swaged in the folded back tips andwelded to the connecting pieces, these attachment points havesignificant strength and their separation is difficult. Additionally, afuse with metal wire as the narrow fusing element has a uniform crosssectional area. Since the cross sectional area of a given metal wiredetermines its resistance, the characteristic of reliable fuse blowingat the specified current, particularly for small currents, is achieved.

Preferably, in the method described above, the wire is bent to align thepair of connecting pieces in a straight or nearly straight line.

Connecting pieces, which connect to the fuse wire, preferably haveadditional processing to provide a fold back at their tips. Wire isinserted in a folded back tip, pressure is applied to swage the wire inthe folded back tip, and the swaged wire is welded. A connecting pieceof this structure can form a strong and reliable connection with wirevia the folded back tip. Additionally, It is preferable to use SUS-304stainless steel wire as the fuse wire,

Still further, the metal plate of the present invention can be formed asa long narrow band and wire can be welded to connecting piece tipregions as metal plate is continuously supplied. For example, thismethod of manufacture can continuously produce fuses via an automatedmanufacturing line. Therefore, manufacturing efficiency can be improvedand low cost production in quantity is possible.

The battery pack of the present invention is provided with a pluralityinterconnected rechargeable batteries disposed in parallel positions,and a fuse connected at both ends to a rechargeable battery electrode toform a series connection with the rechargeable batteries. The fuse isprovided with a metal wire which melts open with a prescribed currentflow, and a pair of connecting pieces which connect to both ends of thewire and are welded to battery electrodes. The tip region of aconnecting piece is bent to provide a folded back tip, and wire iswelded to the connecting piece while inserted in this folded back tip.Furthermore, wire welded at the folded back tips is bent in a directionwhich separates both ends of the connecting pieces attached to both endsof the wire, and the pair of connecting pieces is joined to batteryelectrodes.

A battery pack structured as described above uses a fuse with a lowblow-out current which is also strong with respect to mechanical shock.Therefore, the fuse can reliably blow when excessive current flows, butit will not break due to mechanical shock making high reliability andquality possible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing an example of a prior art fuse.

FIG. 2 is a front view showing a processed metal plate in onemanufacturing step of a fuse in an embodiment of the present invention.

FIG. 3 is an enlarged cross-section view showing the folded back tip ofa connecting piece of the metal plate shown in FIG. 2.

FIG. 4 is a front view showing metal wire set in position on the metalplate shown in FIG. 2.

FIG. 5 is an enlarged cross-section view showing the tip region of aconnecting piece of the metal plate shown in FIG. 4.

FIG. 6 is a front view showing the process step for spot welding tipregions of the connecting pieces of the metal plate shown in FIG. 4.

FIG. 7 is an enlarged cross-section view showing the connecting piecetip region shown in FIG. 5 at spot welding.

FIG. 8 is a front view showing the process step to cut the metal plateshown in FIG. 6.

FIG. 9 is a front view showing the cut connecting pieces bent at thewire into a straight line.

FIG. 10 is an abbreviated diagram showing another embodiment of themethod of fuse manufacture of the present invention.

FIG. 11 is an oblique view of an embodiment of the battery packcontaining a fuse of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2 through 9 show the fuse manufacturing process steps. A fuse isproduced by the manufacturing process steps shown in these figures anddescribed in the following.

[Process Step to Fabricate a Metal Plate]

Metal sheet is cut and worked into the shape shown in FIG. 2 to producea metal plate 1. The metal plate 1 of FIG. 2 is formed in an overalllong narrow shape, the tips of a plurality of rows of connecting pieces2 are separated, and the aft ends of the connecting pieces 2 are joined.Further, the tips of all the connecting pieces 2 are arranged in astraight line. A metal plate 1 of this shape is made by cutting a longnarrow band of sheet metal. The metal plate 1 is made from nickel sheet.However, sheets of metal such as iron, copper, or aluminum, or sheets ofmetal alloys such as brass or steel may also be used for the metal plate1. The surfaces of sheet metals which corrode are plated with nickel orchrome.

The metal plate 1 of the figures is shaped to provide alternating narrowslits 3 and wide slits 4 between connecting pieces 2. The narrow slits 3have the same narrow width along the entire slit. The wide slits 4gradually become wider towards the tips of the connecting pieces 2. Thenarrow silts 3 are the minimum width that allows metal wire 6 cutting.The wide slits 4 are spanned by metal wire 6 joining adjacent connectingpieces 2. Consequently, the width of the wide slits 4 is the length ofthe metal wire 6 for a fuse.

Additionally, as shown in the enlarged cross-section view of FIG. 3,connecting piece 2 tip regions of the metal plate 1 are bent by furtherprocessing to provide folded back tips 5. The folded back tips 5 areformed by further processing to bend the metal sheet after cutting. Thisis because the folded back tips 5 would be crushed by a preceding diecut process step. However, in a method of manufacture which laser cutsmetal sheet to make the metal plate, folded back tips can be provided bylaser cutting after bending one edge of the metal sheet.

[Process Step to Weld on Wire]

As shown in FIG. 4, the metal plate 1 is placed in a fixed position on ametal mount 7, and metal wire 6 is set in the straight line arrangementof connecting piece 2 tip regions. The metal plate 1 shown in FIG. 4 isprovided with two through holes 8, and alignment pins 9 on the metalmount 7 fit in these through holes 8 to locate the metal plate 1 in afixed position on the metal mount 7. As shown in the enlargedcross-section view of FIG. 5, wire 6 is hooked into a fixed position ineach folded back tip provided at the end of each connecting piece 2.Further, to pull the wire 6 into a straight line, both ends of the wireare pulled and temporarily fixed to the metal mount 7 with a prescribedamount of tension. Stainless steel wire is suitable metal wire 6.Specifically, SUS-304 stainless steel wire is optimal. This is becauseSUS-304 is thin and strong as well as having large electrical resistancefor reliable melting at high currents. However, other wire materialsbesides stainless steel, such as aluminum or nickel, may also be used.

Subsequently, as shown in FIG. 6, tip regions of connecting pieces 2 arespot welded to the wire 6 to connect adjacent connecting piece 2 tipregions with wire 6. As shown in FIG. 7, a welding electrode 10 ispressed onto a folded back tip 5 with wire 6 inserted, high current isapplied, and both surfaces of the wire 6 are spot welded to the metalplate 1. During spot welding, the metal mount 7 is used as the otherelectrode. Consequently, a low resistance metal such as copper is usedfor the metal mount 7.

[Cutting Process Step]

As shown in FIG. 8, two adjacent connecting pieces 2 are treated as aunit, wire 6 is cut between each two-connecting piece 2 unit forseparation, and each individual connecting piece 2 is also cut andseparated. Wire 6 is cut at the narrow slits 3 as shown by the arrows inFIG. 8. Further, the metal plate 1 is cut, using a tool such as shears,at the narrow silt 3 and wide slit 4 locations along the broken lineshown in FIG. 8, to detach and separate all connecting pieces 2.

[Process Step to Bend the Wire]

Next, as shown in FIG. 9, metal wire 6, connecting a cut-outtwo-connecting piece 2 unit, is bent in a direction to separate both aftends of the pair of connecting pieces 2 attached at both ends of thewire 6. In the fuse shown in FIG. 9, the wire 6 is bent until the pairof connecting pieces 2 are positioned in a straight line. However, thewire 6 may also be bent to put the pair of connecting pieces in asomewhat inclined position and not bent until they form a straight line.For example, the wire 6 may be bent to form an angle of 90° to 180°between the lengthwise axes of the connecting pieces. The wire 6 shownin FIG. 9 is bent with a small radius of curvature at the tip of eachconnecting piece 2. However, It is also possible to bend the wire with au-shaped bend at its center.

As shown in FIG. 10, the method of fuse manufacture of the presentinvention may also produce fuses in a continuous fashion via anautomated manufacturing line. The manufacturing line shown in FIG. 10continuously supplies metal plate 101 formed in a long narrow band froma drum 14, welds metal wire 106 to the tips of connecting pieces, andcuts the metal plate 101 at prescribed locations to produce fuses.

The drum 14 in FIG. 10 is wound with a long narrow band of metal plate101, which is formed from a further processed long narrow band of sheetmetal. A long band of metal plate 101 is formed, as shown in FIG. 2, byfurther working a band of sheet metal. Namely, a plurality of connectingpieces are formed with separated tips and connected aft ends, and foldedback tips are provided by bending the tip of each connecting piece. Themanufacturing line of FIG. 10 supplies this band of metal plate 101 tothe next process step from a drum 14. However, the manufacturing linemay also provide automated process steps to form a plurality ofconnecting pieces and folded back tips on a band of sheet metal to makea band of metal plate. This manufacturing line continuously supplies aband of sheet metal with no connecting piece or folded back tipprocessing, performs process steps to form a plurality of connectingpieces and folded back tips, and supplies the band to the next processstep.

Metal wire 106 is supplied from a coil of wire 15 and joined to metalplate 101 supplied from a drum 14 in a continuous fashion. The wire coil15 is a coil wound with metal wire 106 which supplies wire 106 in acontinuous fashion, The wire 106 hooks into folded back tips provided atthe ends of the plurality of connecting pieces to set the wire 106 infixed positions on the metal plate 101. Preferably, wire 106 iscontinuously supplied and set on the metal plate 101 with a prescribedamount of tension in the wire 106. Continuously supplied wire 106 set inplace on continuously supplied metal plate 101 is transferred to thenext process step.

The tip regions of connecting pieces are spot welded to weld the wire tothe connecting pieces. A welding electrode 1010 presses down and highcurrent is passed to spot weld both sides of the wire 106, held betweena folded back tip and connecting piece, to the metal plate 101.

Wire 106 welded to the metal plate 101 is cut at prescribed locations bya cutting machine 16. As shown in FIG. 8, two adjacent connecting pieces2 are treated as a unit, the cutting machine 16 cuts wire between eachtwo-connecting piece 2 unit for separation, and also cuts and separateseach individual connecting piece 2. Wire 6 is cut at the narrow slits 3as shown by the arrows in FIG. 8 and connecting pieces 2 are cut andseparated along the broken line shown in FIG. 8. Next, as shown in FIG.9, wire, connecting a cut-out two-connecting piece 2 unit, is bent in adirection to separate both aft ends of the pair of connecting pieces 2and position them in a straight line.

FIG. 11 shows a battery pack containing a fuse manufactured by theprocess described above. In the battery pack of FIG. 11, both ends of afuse are spot welded to the electrodes 12 of two rechargeable batteries11, fastened parallel to each other, to electrically connect therechargeable batteries 11 in series. The rechargeable batteries 11 ofthe battery pack shown in FIG. 11 are fixed in a parallel disposition byheat-shrink tubing 13. The rechargeable batteries 11 may also be bondedor pressure fit in a case to fix their positions, The batteries 11 arearranged and connected such that their electrodes 12, which areconnected by a fuse, lie in the same plane. Although the battery pack ofFIG. 11 is provided with two rechargeable batteries 11, there may bethree or more batteries.

A fuse has connecting pieces 112 welded to both ends of a metal wire116. Each connecting piece 112 of the fuse in FIG. 11 is spot welded attwo locations for connection to the electrodes 12. The two long narrowconnecting pieces 112 are arranged in a straight line, and wire 116 iswelded to their opposing tips. The wire 116, which is welded to theconnecting pieces 112, is bent in a direction to separate both aft endsof the connecting pieces 112 attached at both ends of the wire 116. Themetal wire 116 has both end regions oriented parallel to each other, andconnecting pieces 112 are attached to both these end regions. The wire116 shown in FIG. 11 is curved at its center region and both end regionshave a parallel orientation. However, the center region of the wire mayalso have a straight line configuration, and both end regions may bebent at right angles and joined to the connecting pieces.

A fuse which uses SUS-304 stainless steel wire as its metal wire 116 canhave a blow-out current setting of 5A for a wire diameter of 0.2 mm, andcan have a blow-out current setting of 3A for a wire diameter of 0.15mm. SUS-304 stainless steel wire has a strength applicable for use insprings, and has the characteristic that it is thin and mechanicallystrong.

A battery pack provided with three or more rechargeable batteriesconnects electrodes of two rows of batteries by a fuse, and connectsother electrodes by conducting leads to join all the batteries. Nickelsheet, or nickel or chrome plated sheet metal such as iron, copper, orbrass can be used as the conducting leads. In addition, all thebatteries of a battery pack housing three or more batteries may beconnected in series via fuses. Finally, four or more batteries may beconnected in series via a plurality of fuses and leads.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within themeets and bounds of the claims or equivalence of such meets and boundsthereof are therefore intended to be embraced by the claims.

What is claimed is:
 1. A method of fuse manufacture comprising:fabricating a metal plate with an overall long narrow shape, with aplurality of rows of connecting pieces having separated tips andconnected aft ends, and with the tip of each connecting piece arrangedin a straight line; connecting tip regions of adjacent connecting piecesby welding metal wire to the connecting piece tip regions which arearranged in a straight line; treating two adjacent connecting pieces asa unit, to cut the wire between each two-connecting piece unit forseparation, and to detach each individual connecting piece; bending thewire connecting each cut two-connecting piece unit in a direction whichseparates both ends of the pair of connecting pieces attached to bothsides of the wire; and further processing the connecting piece tipregions to provide folded back tips, inserting wire inside the foldedback tips, and swaging and welding the wire via the folded back tips. 2.A method of fuse manufacture as recited in claim 1 wherein nickel sheetmetal is used as the metal plate.
 3. A method of fuse manufacture asrecited in claim 1 wherein one material is selected from iron, copper,or aluminum sheet metal, or from alloy sheet metal such as brass orstainless steel, and is used as the metal plate.
 4. A method of fusemanufacture as recited in claim 1 wherein the metal wire is bent untilthe pair of connecting pieces are positioned in a straight or nearlystraight line.
 5. A method of fuse manufacture as recited in claim 1wherein narrow slits and wide slits are established in an alternatingpattern in the metal plate, adjacent connecting pieces are grouped bythe slits, and wire is cut in the narrow slits.
 6. A method of fusemanufacture as recited in claim 5 wherein the narrow slits have uniformwidth overall, and the wide slits gradually become wider towardsconnecting piece tips.
 7. A method of fuse manufacture as recited inclaim 1 wherein stainless steel wire is used as the metal wire.
 8. Amethod of fuse manufacture as recited in claim 7 wherein SUS-304stainless steel wire is used as the metal wire.
 9. A method of fusemanufacture as recited in claim 1 wherein either aluminum wire or nickelwire is selected and used as the metal wire.
 10. A battery packcomprising: (a) a plurality of interconnected rechargeable batteriesfixed in parallel orientation; (b) a fuse connected at both ends to arechargeable battery electrode to connect the rechargeable batteries inseries; said fuse further comprising: metal wire which melts open with aprescribed current flow; a pair of connecting pieces attached to bothends of the wire and welded to battery electrodes; and wherein the tipregions of connecting pieces are bent to provide folded back tips, wireis welded while being held inside these folded back tips, further, wirewhich is welded in the folded back tips is bent in a direction whichseparates both ends of the pair of connecting pieces attached to bothsides of the wire, and the pair of connecting pieces is connected tobattery electrodes.
 11. A battery pack as recited in claim 10 whereinthe metal wire is bent until the pair of connecting pieces arepositioned in a straight or nearly straight line.
 12. A battery pack asrecited in claim 10 wherein the fuse connecting pieces are nickel sheetmetal.
 13. A battery pack as recited in claim 10 wherein the fuseconnecting pieces are one material selected from iron, copper, oraluminum sheet metal, or from alloy sheet metal such as brass orstainless steel.
 14. A battery pack as recited in claim 10 wherein themetal wire of the fuse is stainless steel wire.
 15. A battery pack asrecited in claim 14 wherein the metal wire of the fuse is SUS-304stainless steel wire.
 16. A battery pack as recited in claim 10 whereinthe metal wire of the fuse is selected from either aluminum wire ornickel wire.